1. Field of the Invention
The present invention relates to a high-pressure gas operated setting tool including a piston guide, a driving piston, axially displaceable in the piston guide and formed of a head and a stem, and a return element surrounding the stem and extending between a stop provided in a front, in a setting direction, end portion of the piston guide and a front, in the setting direction, end surface of the head.
2. Description of the Prior Art
German Publication DE-OS 1,939,801 discloses an explosive powder charge operated setting tool for setting nail-shaped fastening elements in a base, with the driving piston of the tool being returned to its initial position, after a setting process, by an elastic sleeve. The returning elastic sleeve surrounds the stem of the driving piston and extends between a stop, which is provided in the front, in the setting direction, end portion of the piston guide, and the front, in the setting direction, end surface of the driving piston head.
In this setting tool, the difference between the outer diameter of the return element and the inner diameter of the piston guide is large. This difference results from the fact that the return sleeve is formed of a material with high lateral expansion. This means that the reduced, in the axial direction, volume of the sleeve, is enlarged in the radial direction until the sleeve expands radially to the inner wall of the piston guide.
The largest possible axial return path of the return element and, thus, the maximum possible axial displacement of the driving piston depends on the free space between the return element and the inner wall of the piston guide.
The resiliency characteristics of the return sleeve, which is disclosed in DE-OS 1,939,801, permits a maximum reduction of the original length of the sleeve upon the sleeve compression, by half. To be able to provide for a large axial displacement of the driving piston, the increase of the empty cylindrical volume is necessary. This volume can be increased by increasing radially the guide bore of the piston guide, i.e., by increasing the free volume between the return element and the inner wall of the piston guide. A big drawback of this approach consists in that the dimensions of the setting tool are substantially increased which makes the handling of the setting tool impossible. If, e.g., a rubber is used for manufacturing the sleeve, then the relatively long sleeve has an increased own weight. The large weight of the sleeve negatively affects the entire weight of the setting tool and increases the nose-heaviness of the setting tool.
Accordingly, the object of the invention is a high pressure gas operated setting tool that can be economically produced, has a reliable, long-lasting piston guide for the driving piston, has small dimensions, and is easy to handle.